In principle, all the materials used in the manufacture of enclosures or dwellings being qualified to resist fire during predetermined period of time must meet a series of particular requirements. These requirements include stability, resistance, insulation and lack of toxicity.
With regard to stability, all the materials should behave in a stable way in the presence of a fire, that is to say, they should not lose the mechanical features that existed before the existence of a fire.
In relation to resistance, the materials should have a high flame and fire resistance. With regard to insulation, the materials used must be heat insulating.
Lastly, as for toxicity, these materials should not give off, at any moment, toxic or inflammable gases, even during the combustion.
Up till now, it has been thought that those materials presenting the above mentioned conditions are conventional incombustible materials. This assumes that their incombustibleness can eliminate any danger in case of a fire.
Nevertheless, it has been proved that the characteristics of the above mentioned materials are not accurate, since for a building material to provide safety in the presence of a fire, it is very important that it retains, in an essential way, its shape and resistance in the fire, relying on a thermal conductivity which is markedly low.
A material having these conditions is, undoubtedly, preferred to another material which may not burn, but loses its resistance quickly when submitted to the action of fire.
This reasoning is based on the fact that, in a building construction, the function of the materials is to support it and, consequently, to create a space to be used as a room, warehouse, etc. If they still maintain this function, even in case of a fire, they are valid, even if they can burn.
On the other hand, if they own these properties, they will allow the persons and materials protected by them to be more easily saved, and also they will permit to go into action the fire extinguishing system existing in the enclosure.
By way of example, it can be asserted that, at present, firemen do prefer to intervene in a fire with wooden stairs and structures than in a building having mechanical stairs and structures or with masonry works. In the first case, firemen can take preventive measures, knowing the ground on which they are acting. In the other two latter cases, the materials, when heated by the fire action, make the transit difficult, they crack open and collapse without warning.
Consequently, wood is proving to be, at present, one of the most adequate materials to control a fire.
Wood is one of the materials better combining the above mentioned four qualities, namely: stability, resistance, insulation and lack of toxicity. Nevertheless, the downtrend in using wood in the building industry has been due, mostly, to the poor quality of the material used.
Also, the inadequate application of wood, often discredited by many builders, has had an influence on the lack of utilization of same. Nevertheless, the introduction of new technologies and new materials allows a harmonic conjunction of same, creating the appearance of a new product, which, used in an adequate way, can act preventing a fire. It also provides valuable time for saving both persons and materials protected by same, allowing for the fire extinguishing system to be put in action.
Obviously, the use of wood as a material for building or manufacturing fire-resistive enclosures must rely on a greater resistance, both as regard the flexion and the compression, a annulment and reduction of thermal conductivity and expansion, and, at the same time, a reduction and annulment of dimensional variations, that is to say, contractions and expansions.
It should be pointed out that, in an axial sense, the dimensional variations of wood, in parallel to the fibers, and under the effect of the humidity changes, are practically null.
Also, the wood used must improve both inertia and its mechanical characteristics. Its temperature must be constant. This allows the assembly of different parts, both if they are bonded by gluing, and by using nails, screws, pegs, etc.
The above mentioned method for building fire-resistive enclosure can be also applied to access doors or to doors installed in dwellings, which must meet the mentioned characteristics.
Nevertheless, until now, nothing is known about the existence of a new enclosure fire-resistive for a predetermined period of time, fitted with doors also fire-resistive, the material of which, used in a basic manner, is wood.